Straight Stitch Foot
This foot is exactly as it sounds. Your straight stitch foot will be used the most. It also will be the foot you use to do most of your zig zag stitches.
Zipper Foot
This foot is used for zippers, piping and sewing seams that have excess bulk on one side.It can adjust from one side of the needle to the other for a close seam.

Invisible Zipper Foot
Invisible zipper foot is a special foot that puts in an
invisible zipper.

Invisible zipper installation link
Gathering Foot
Gathering can be done by sewing two straight stitches parallel to each other at 2/8" and 4/8" from the seam edge. Then pulling the underside threads, you begin to gather your
fabric.
An alternative method to gathering is the gathering foot you see below. This very handy tool is great when you have a lot of gathering to do. I have made dresses with a lot frills and put after market frills on bed skirts that would have been pain staking if I did not have this foot.
The fabric is placed under the gathering plate and it pushes the fabric through. Your gathers are done in one step and faster than if you did it by hand.

Buttonhole

The buttonhole sewing attachment above, measures the button and creates the buttonhole for the size needed. It does this all in one step for saving time. You can also adjust most button attachments manually, when the button is too large to fit the attachment.

The vintage buttonhole attachment on the right comes with the plates shown above.
These older sewing machine attachments were a little more bulky to work with, and took more time to set up, but they were very effective.
I first learned to sew, and made many of my first sewing projects on this type of machine, using this type of buttonhole attachment.
In fact my mom still has and uses her Singer machine from the 1950's. She has more than one modern machine, that has more options, but loves the older work horse mentality of her old Singer.
Roller Foot
The roller foot is great for leather, vinyl, and suede. These types of materials can be difficult because the two layers tend to shift. A regular straight stitch foot will cause friction pressing down on the material and causing it to get caught up in the feed dogs of your machine. The material is soft and playable so it does not feed smoothly.
With the roller foot it does exactly what the name implies, it rollers over top of the material and gives a smooth feed with less friction. Like a rolling pin over sticky pie dough. This foot is also very useful for heavy weight fabrics, such as denim and canvas that have bulky and uneven seams.
This is a rolled hem foot for your sewing machine. This foot makes 1/4" hems on most
fabrics

Blind Hem Foot

This foot replaces the hand sewing method. It is a fast way of hemming dress slacks.When the hem is positioned correctly, the needle and thread only catch the fabric every few stitches for a seemingly stitch less hem.
For sewing machine attachments alternatives, see hand sewing needles.
Walking Foot

This useful machine attachment is great for fabrics like plaids and stripes or patterns that need to match up
on the finished projects. The top and bottom layer of fabrics remain evenly stitched.
It is also useful for vinyl and bulky knits that tend to stretch or slip when sewing.
Over Edge Foot

If you don't have a serger, the over edge foot can give the next best alternative to a serger finished seam.
The above mentioned, is only a small amount of sewing machine attachments available. Depending on what make and model of sewing machine you have. Machine attachments really open up the variety of details you can accomplish and make adding detail more pleasurable when you have the right tool.
Most of these attachments are not expensive and if you purchase them one at a time or as needed, they become a indispensable partof your sewing world. In other words once you have them they are yours forever.
Click here for fantastic video tutorials for sewing attachments.